Posting an error-riddled translation is worse than posting no translation. If a group or translator does good work on a series and drops it, any other group can just pick up where they left off. If you post bad translations, either another group is just going to have to redo it properly or the readers will be confused when major plot threads make no sense (and might blame the author for that). Not to mention that posting any translation at all will nudge other groups away from working on it to avoid duplicating work and stepping on toes.
If your translation relies heavily on guesswork, either get some help from another translator or just keep it to yourself.